It's not unheard of for new plane types to experience glitches early in their life spans

In the aftermath of the crash of Lion Air Flight 610, one of the worst air disasters in recent years, many observers are asking: How could a brand-new, state-of-the-art plane from one of the world’s leading manufacturers fall from the sky 13 minutes after takeoff—especially since there were no other obvious risk factors at play?

The plane had been serviced for a technical problem the day before the flight took off, which reportedly involved airspeed and altitude indicators, but Lion Air executives said the matter was resolved, and the plane was cleared to take off the next morning. (In the wake of the crash, Indonesia ordered an inspection of all Boeing 737 Max 8s belonging to national commercial airlines, reports CNN; investigators at the scene will also include experts from Boeing and the National Transportation Safety Board.)

The advanced, fuel-efficient Max model has been flying commercially since 2017, and it’s already on track to be fastest-selling airplane in Boeing’s history—with 4,700 orders on the books, from airlines including Southwest, United, Alaska Airlines, American Airlines, and Norwegian. The single-aisle 737 is a workhorse of commercial airlines around the world: it’s been operating for 40 years, and there are more than 10,000 currently in service; a 737 takes off somewhere in the world every two seconds, according to Boeing. “It is a highly reliable, very forgiving airplane,” says Captain Mark Weiss, an aviation consultant, who flew similar planes—Boeing 737s and 777s—during his years as a pilot for a major airline. John Goglia, an aviation consultant and former member of the National Transportation Safety Board, agrees, noting that though air traffic control tapes from the Lion Air flight show an erratic series of maneuvers, “I don’t think this should affect overall confidence in the airworthiness of the plane.”

Even before a new airplane model carries its first paying customer, it undergoes years of rigorous tests under extreme conditions. A typical plane is composed of thousands of parts involving hundreds of different outside vendors. The 737 alone is made up of 367,000 parts, which are assembled at a plant outside Seattle, but Boeing doesn’t make the seats or engines itself, it outsources this work to specialist vendors who produce much of what goes inside the plane, down to the carpeting and seat-back TVs.

It’s not unheard of for new plane types to experience glitches early in their life spans

It’s not unheard of for new plane types to experience glitches early in their life spans

Each of the plane’s components is subject to all sorts of abuse: for example, to test how well a jet could withstand everything from a hail storm to a bird strike, engines are pelted with a barrage of ice chunks and dead chickens. The fuselage, wings, and other large plane parts must pass fatigue testing to see how they’ll respond to stressors like frequent takeoffs and landings, and they also get jolted with electricity equivalent to a lightning strike. Test flying, which takes place typically in the year running up to the first delivery, entails taking the plane to extreme temperature zones, both hot and cold, like northern Canada during the depths of the winter. At all stages of the process, the aircraft manufacturer, as well as the many other separate companies that produce engines, avionics, and many other key parts are overseen by the regulators who must finally sign off on certification—in the U.S., the Federal Aviation Administration.

Even so, it’s not unheard of for new plane types to experience glitches early in their life spans, although they rarely lead to fatal crashes. Take the case of the Boeing 787 Dreamliner, which the FAA grounded in 2013—in its first year of service—following a string of incidents in which the plane’s lithium batteries caught fire. The action affected more than 100 flights a day and not only had a serious impact on international travel, but called into question the safety of the plane itself. The batteries were found to be prone to overheating; the planes were returned to service after Boeing designed a new system to encase the batteries to better contain fire and smoke.

Years earlier, in 2010, a Qantas Airbus A380, the world’s largest plane, suffered an uncontained engine failure after taking off from Singapore for Australia; pilots succeeded in landing the crippled plane safely back at Changi. The rest of the Qantas A380 fleet was grounded, and several other airlines temporarily followed suit, while attention was focused on the jet’s Rolls-Royce Trent 900 engines. A number of the engines were ultimately replaced after inspections revealed a manufacturing flaw, and the worldwide fleet was declared safe.

In the end, what the most recent tragedy may show yet again is that most aviation accidents are shown to be the result of a complex series of events.

“Accidents don’t happen for a single cause,” says Weiss. “There are typically multiple factors involved that generally become a cascading effect.”